15mm f/2.8 Fisheye II (non-L)
Yes, I kept my 15mm f/2.8 fisheye when the 8-15mm f/4 L fisheye zoom was released for three reasons:
1) DxO doesn't support the 8-15mm f/4. It was listed as to be supported, delayed again & again, until the lens was released, then it was dropped permanently from the list.
2) I use the 15mm f/2.8 in low light to capture a whole stage while standing right in front of it. One more aperture stop will always make for a cleaner image by shooting one ISO stop lower.
I've heard the the 8-15mm f/4 has better IQ. The lack of DxO support makes me wonder how true is that, as in maybe the distortion is so bad, DxO can't fix it, or something.
3) I'm not sure whether I'd find any use for focal lengths between 8 & 15. Actually, I'm considering selling my Sigma 8mm circular fisheye prime.
I'll be happy to see an EF 15mm f/2.8 II with better IQ.